基于声发射波形分析的锦屏大理岩岩爆试验研究

岩爆破坏是一种非常复杂的非线性力学行为,影响岩爆的因素众多。文章通过对锦屏大理岩进行两例全程破坏和一例非全程破坏岩爆试验,采集试验过程中的应力和声发射参数,以应力曲线和声发射累计能量曲线为基础确定了关键点,并针对关键点对岩爆过程中的声发射波形进行分析,得到了锦屏大理岩发生岩爆的本质规律。结果表明,锦屏大理岩在单位时间内的声发射波形数分布与关键点有很大相关性,单波占绝大多数,双波、三波和四波在关键点处分布较为集中,多波只在岩爆时刻出现;锦屏大理岩在岩爆阶段与前期加载阶段相比,会有单位时间内波形数数不清的岩爆波产生,是其岩爆阶段的独有特征。     

完整围岩剪切型岩爆发生的力学机制

文章根据大量工程岩爆实例,总结剪切型岩爆的特征,在此基础上提出一个剪切型岩爆的简化力学模型,在考虑岩爆区岩体自身能量释放的基础上,结合Cook刚度理论对剪切型岩爆发生的物理力学过程进行研究,分析由于潜在剪切破裂面本构曲线峰后软化现象而产生的围岩结构失稳,以及失稳阶段围岩结构对外界的能量释放,对剪切型岩爆的非稳定性机制进行探讨。研究结果表明:剪切型岩爆可以看成是由于开挖应力集中作用下潜在剪切破裂面剪切错动滑移,引起自身及周围完整岩体能量突然急剧释放,导致岩爆区岩体破碎并向开挖临空面抛掷的现象。岩爆区岩体及周围完整岩体所释放的能量对剪切面的作用相当一对串联弹簧的作用效用。剪切型岩爆的发生受岩性、潜在剪切破裂角、剪切面周围岩体刚度的控制作用,是围岩受力变形过程中岩石材料力学性质渐进性劣化导致的一种能量释放驱动下的围岩状态失稳突跳现象。     

白云岩力学压缩试验及声发射规律研究

在高地应力近水平岩层中开挖隧道时,由于近水平层理的构造特征,隧道极易出现拱顶离层、掉块、局部超挖、支护结构偏压、初期支护混凝土开裂等现象,甚至发生拱顶失稳坍塌事故。为研究高地应力近水平岩层的破坏特征,本文以大峡谷隧道为工程背景,通过现场钻孔取芯,对岩样进行常规压缩试验,并借助声发射系统分析了岩样压缩破坏过程。研究结果表明：岩石的破坏过程可分为裂纹压密和弹性变形阶段、塑性阶段、峰值阶段、残余阶段;岩样在低围压下主要为张拉劈裂破坏,在中围压下为张拉劈裂破坏和剪切破坏共同存在,在高围压下主要呈剪切破坏且破裂岩体的裂纹扩展更为显著。     

基于能量法的浇注式沥青混合料疲劳特性分析

浇注式沥青混合料的材料及组成与常规沥青混合料存在较大差异,对浇注式沥青混合料GA10进行了不同应变水平、不同温度条件下的四点弯曲疲劳对比试验,建立疲劳次数与应变相关的疲劳方程,并采用累计耗散能和累计耗散能比DER对GA10在不同温度下的能量变化趋势进行分析。结果表明:疲劳方程能很好地表征了沥青混合料的疲劳行为,疲劳次数随温度的升高疲劳寿命增加;而随着应变水平的增加,则引发沥青混合料疲劳次数成倍减少;以三阶段分析疲劳破坏初始劲度模量累计耗散能指标与温度、应变并不是单一变量关系,且以初始精度模量下降到50%为破坏条件不具有准确性。     

大埋深、高地应力地下洞室群围岩破坏机理及应对措施研究

地下洞室开挖过程中,脆性围岩应力释放型破坏(岩爆、片帮掉块等)和结构面—应力型破坏(围岩松弛、喷层开裂、顶拱坍塌等)是洞室群围岩破坏常见的主要形式。文章以白鹤滩水电站左岸尾水连接管洞室群为研究对象,结合现场踏勘统计分析,基于500μm显微镜观察、室内岩石力学单轴压缩试验对围岩应力释放型破坏机理进行了研究,基于数值模拟、孔内摄像技术对围岩结构面—应力型破坏机理进行了研究,并分别提出了相应的应对措施。研究表明,完整性较好的脆性围岩(Ⅱ类)具有一定的塑性性能,洞室开挖卸荷后岩体易发生压剪破坏,产生与受力方向呈小夹角的破坏面,塑性势能沿破裂面释放,进而引起薄层掉块或岩爆现象;对于完整性较差的围岩(Ⅲ类),由于节理、错动带等裂隙的存在,多表现为岩性强度高、岩体强度低的性状。围岩微裂纹在高地应力作用下逐渐扩展连通,形成相互切割的结构面,并逐步向岩体深部不断发展,直至应力完全释放,受周边洞室爆破振动影响时易发生坍塌现象,破坏过程在宏观上表现为由表及里并具时效性的特点。     

基于电化学阻抗法的温度对管道腐蚀影响

研究管道的腐蚀行为对预防管道腐蚀,减少材料浪费和经济损失有很大的意义。文中采用电化学阻抗法,研究在不同温度下(40~65℃)某油田采出水对管线钢材质试片的腐蚀规律。试验结果表明:随着温度的升高,管线钢试片的腐蚀逐渐加剧,在60℃时对试片的腐蚀影响最大,温度继续升高,对试片的腐蚀减小。     

油-水两相流流变特性研究

应用细管式流变仪对含水稠油流变性进行了实验研究,得出不同温度、不同含水率以及不同剪切率下的流变规律和计算方法。在实验范围内含水稠油为非牛顿流体。随着温度的升高,流变指数增大而稠度系数减小;随着含水率的增加,流变指数和稠度系数不断减小。含水稠油的温度在90℃以下时,其n值都小于1,此时含水稠油的流变特性为假塑性流体,而且,温度越低,n值越小,表示含水稠油的流变特性偏离牛顿流体特性越远,假塑性越强。     

基于改进动力强度折减法的隧道地震破坏机理探讨

文章分析了影响隧道在地震作用下破坏的因素,研究了不同围岩级别、不同跨度、不同结构形式和不同埋深等条件下隧道结构在地震中的破坏机理,分别针对各个影响因素进行了对比分析;通过静动力转换边界将静力场施加到动力计算中作为初始应力条件,对动力强度折减法进行了改进,通过计算应用证明了其可行性;使用改进的动力强度折减法对深、浅埋隧道在地震作用下的破坏机理进行了计算分析。结果表明,不同埋深隧道在地震中的破坏过程不同,浅埋隧道是从隧道上方两侧开始破坏的,逐渐形成贯通到地面的破裂面;深埋隧道最先在4个边角的应力集中处出现塑性应变,顶部和底部的塑性应变较小,随后从两侧开始逐渐形成贯通的塑性应变区,直至破坏。     

温度和拉伸变形对双相不锈钢析出相的影响

文中对未变形和拉伸变形后的样品分别进行750℃、850℃、950℃、1 050℃及1 150℃的固溶处理,通过金相显微镜观察样品在室温及不同温度下显微组织和σ相析出量的变化;分析不同状态下样品的硬度值变化。综上得出结论为单纯较大的拉伸形变不会使样品产生σ相,但较大的拉伸变形会细化晶粒尺寸,改变铁素体形态,加速铁素体的生成;随着温度的升高(750～950℃),未变形样品和拉伸变形后的样品中σ相含量均会逐渐增大,拉伸形变后的样品中σ相含量要大于未变形样品,到1 150℃时,σ相全部消失;温度升高均发生了奥氏体向铁素体的转变;σ相对材料硬度影响不大,从950℃到1 050℃温度范围内,拉伸变形后样品硬度值下降幅度大于未变形样品。     

循环冲击荷载下喷射混凝土的动态力学性能及破坏模式研究

地下空间中频繁的动态荷载扰动会对支护结构的安全造成严重威胁。为探究喷射混凝土在高应变率循环冲击荷载下的动态力学性能变化和破坏模式,本文依托老营盘隧道,采用直径50mm的分离式霍普金森压杆（Split Hopkinson Pressure Bar,SHPB）对混凝土试件开展循环冲击试验,从应力—应变行为、动态力学性能指标、能量转化规律、破坏模式等方面进行分析。研究结果表明,随着冲击次数增加,喷射混凝土峰值应力逐渐减小、极限应变和平均应变率逐渐增大;喷射混凝土吸收能基本不变,反射能增加、透射能降低;冲击过程中喷射混凝土试件中心细长微裂缝逐渐发育并增多,裂缝从外侧向中心处延伸,最后裂缝贯穿整个混凝土结构,发生突变破坏。     

Survey of R&D in PRT systems

A survey of research and development in advanced transit has been made by Chalmers University of Technology in Gothenburg in cooperation with Trans21 in Boston. Summary findings are reported for fourteen academic research programs and ten development programs for PRT. An earlier version of this paper was presented at the International Conference of PRT and other Emerging Systems held in Minneapolis in 1996.     

The Impact of Container Type Diversification on Regional British Port Development Strategies

Abstract

Despite a concentration of container traffic in the southeast of the UK over the last few decades, regional ports are attempting new development strategies to capture or retain specific traffic segments. These include intra-European short-sea traffic and a potentially increasing feeder market. These trends are reflected in the movement of different container types, which result in a number of planning challenges related to changing infrastructural and operational requirements. This paper uses highly disaggregated data on container type movements to address three issues that can inform these planning challenges. First, the imbalance of trade resulting in empty container repositioning; second, the requirement for gauge-cleared rail routes to cater for the increasing proportion of high-cube containers; and third, the specialisation of European short-sea traffic at secondary UK ports. The results reveal the disproportionate repositioning of empty containers at Scottish ports and the importance of 45?ft, high-cube and pallet-wide containers at regional ports, highlighting their focus on intra-European short-sea traffic and raising difficulties relating to their lower quality of landside infrastructure (particularly rail) in comparison to the large south-eastern ports. The potential repercussions on hinterland infrastructure development raise questions about both public and private sector responses to regional port development.     

管道风险分析指数评分法中分值调整初探

管道风险分析指数评分法中重要步骤之一就是确定影响管道事故因素的权重,各个管道风险因素在整个管道事故中所占的权重是不相同的。针对目前管道风险分析指数评分法基本假设之一（各因素的分值范围都是0～100分）,为了更加客观、准确、合理地反映各个风险因素对于管道事故的影响程度,提出并论述了依据层次分析法的数学逻辑性进行综合计算得出管道风险因素的权重,然后对评分法中各个因素的最高分值,根据其权重不同进行相应调整,从而增强评价者对风险因素的认识和评判能力,提高管道风险评价结果的准确性。     

A century of evolution of the accessibility concept

The concept of accessibility has acquired numerous meanings along multiple dimensions during the century of its evolution. This essay argues for the salience of two dimensions: application-based and definition-based. In its application, accessibility has incorporated positive and normative dimensions which have varied in prominence over time. In its definition, accessibility has varied between a mode of evaluation incorporating measured mobility and proximity, on the one hand, and a predefined market basket of urbanist improvements to transportation and land use systems, on the other. Advocates of the accessibility shift should emphasize both the measured approach to accessibility and accessibility’s normative side.     

天然气站往复式压缩机活塞失效分析

针对天然气站往复式压缩机活塞的断裂事故,运用失效分析方法,开展了活塞断口扫描电镜分析、能谱和金相分析。根据断口形貌的电镜和金相观察结果,结合理论知识,分析确定了该活塞发生断裂事故的主要原因,即在特定工况下该活塞的材料缺陷是造成断裂的主要因素。     

中国城市道路规划方位性问题研究

文章结合中国的传统建筑文化理念和现代科学原理,从历史文化、能源节约、环境保护、房地产定价、交通安全等多方面分析研究了城市道路在规划和设计时所应遵从的定向规则。     

Predicting queue variability to enable analysis of overload risk

ABSTRACT

Predicting the risk of traffic demands and delays exceeding critical limits at road junctions, airports, hospitals, etc., requires knowing how both mean and variance of queue size vary over time. Microscopic simulation can explore variability but is computationally demanding and gives only sample results. A computationally efficient approximation to the mean is used in many modelling tools, but only empirical extensions for variance in particular situations have been available. The paper derives theoretical formulae for time-dependent and equilibrium variance, believed to be novel and to apply generally to queues covered by the Pollaczek–Khinchin mean formula, and offering possible structural insights. These are applied in an extended approximation giving mutually consistent mean and variance estimates with improved accuracy. Tests on oversaturated peak demand cases are compared with Markov probabilistic simulation, demonstrating accuracy (R^2?>?0.99) for typical random, priority-like (M/M/1) and traffic-signal-like (M/D/1) queues. Implications for risk analysis, planning and policy are considered.     

Planning guidelines for metro–bus interchanges by means of a pedestrian microsimulation model

The big paradigm for cities nowadays is to study the movement of pedestrians at the interface between metro and bus systems – metro–bus interchanges. When these interchanges are not well designed, walking is inefficient and can be unsafe for pedestrians. This paper analyses, by means of a pedestrian microsimulation model, metro–bus interchange spaces in order to propose planning guidelines for the city of Santiago de Chile. Specific objectives are (1) to identify the variables that provide efficiency and safety in those spaces; (2) to simulate different scenarios using the pedestrian simulation model LEGION; (3) to propose planning and design guidelines for pedestrian spaces at metro–bus interchanges; and (4) to contrast the recommendations in the recently opened terminal station on Line 1 of Metro de Santiago: Los Dominicos Station.     

生命大过天

文章介绍了广西壮族自治区公路管理局开展专项行动,治理以桥梁为重点的交通基础设施安全隐患的情况,针对在役桥梁、在建桥梁和农村公路桥梁存在的安全隐患提出了相应的治理措施。